1. Field of the Invention
This invention relates to pipe fittings and, more particularly, to a pipe fitting made of an electrically non-conducting material in which conducting means are provided for bonding and grounding purposes or to insure electrical continuity for the pipes being connected by the fitting.
In the field of telephone communications, and particularly with reference to underground installations, much use is made of pressurized cables. The rational for using a pressurized system is that by maintaining cables under pressure, particularly when dry air is used as the working fluid, conductors contained therein are, to a great extent, shielded from the effects of surrounding moisture and fluids permeating the ground through which the cables pass. Specifically, such moisture and fluids are prevented from penetrating pressurized cables by virtue of the pneumatic pressure therein which tends to serve as a barrier against the entry of moisture and other contaminants.
In present day practice, cable pressures are boosted at selected locations, usually manholes, along an underground cable route by manifolding the individual pressurized cables to a paralleling aluminum-lined polyethylene pipe which carries pressurized dry air from an air drier in the central office of the system. By maintaining a relatively high pipe pressure and a high available gas flow through the air pipe, a dry air source, in effect, is produced at the manifold locations in the manholes. The air pipes run between manholes and in each manhole the pipe ends are joined with a special fitting equipped with a threaded port for a pressure testing valve. This valve provides a pressure point for plotting the air pipe gradient, a facility for buffering under special conditions, and a means of providing emergency pressure protection for section replacements.
In general, the pipe fitting of this invention relates to the abovementioned special pipe fitting. Conventionally, these special pipe fittings are fabricated out of stainless steel or a tinned corrosion resistant metal. For reasons of cost and other factors, attempts have been made to replace these metal fittings with fittings made of the presently available tough, non-corrosive plastics. These plastics have proved to be eminently suitable for the purpose, but they have one major drawback; the best plastics for the job are non-conductors of electricity. Because it is a requirement to have a current path through the fitting not only to insure continuity with the aluminum lining of the pipes being connected, but also to reduce galvanic corrosion and to provide means to electrically bond and ground the fitting, it becomes necessary to incorporate a conductor in the fitting so that these functions can be accomplished.
2. Description of the Prior Art
Generally, in the prior art, the problem of providing a conductive path across an electrically non-conducting pipe fitting has been solved by incorporating a metallic conducting sleeve inside the bore of the fitting with the ends of the sleeve projecting out of the coupling ends of the fitting such that electrical contact is made with the aluminum lining of the bores of the pipes being connected. Although this expedient satisfies the requirement for electrical continuity across the fitting, it adds appreciably to the cost thereof and does not solve the problem of providing grounding or bonding means for the fitting. The problem has been met in these prior art fittings by providing a grounding post which penetrates the wall of the fitting and contacts the longitudinal conducting sleeve in the bore thereof. The exterior end of the post is threaded to receive a nut which is used to secure a grounding wire or bonding ribbon on the fitting. These designs have a drawback in that the nut is an extra part and there is always a possibility that it will be lost. Further, in some designs, a crimping tool, not normally carried has to be available to the serviceman for use in installing the air pipe fitting to provide a suitable ground bond connection. In addition, in underground cable service, the aluminum lining of the pipes being connected has a protective coating and the lining also is subject to a build-up of foreign matter; thus, a problem in establishing good electrical contact is presented. This coating and surface build-up has to be removed without, of course, damage to the aluminum lining itself. Preferably, also, there should not be a requirement for a special tool for that purpose. The prior art does not show a fitting that meets the requirements for a rugged, low-cost, non-corrosive fitting nor one provided with means to insure that a good electrical contact is made when pipes are connected.